Process for making methylol coumarin



United States Patent 3,349,101 PROCESS FOR MAKING METHYLOL COUMARIN Sidney C. Beach, Huntington, W. Va., assignor to The McGean Chemical Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Filed Feb. 14, 1966, Ser. No. 527,042

7 Claims. (Cl. 260-4432) This invention pertains to a process for making methylol coumarins useful as brightening agents in acidic nickel plating baths. The use of methylol derivatives of coumarin as brightening and leveling agents in nickel plating baths, wherein the substituent methylol group is attached to the 5, 6, 7 or 8 positions of the coumarin nucleus, is described in US. Patent No. 2,986,501 issued May 30, 1961, to Bernard P. Martin. The present invention is concerned with an improved method of producing that material, and more especially of the mono and di-substituted compounds.

The previously known methods of preparing methylol coumarins do not provide a commercially practical or economic procedure for their production in the quantities needed for industrial nickel plating use, and it is accordingly a primary object of the invention to disclose a method of producing these coumarin derivatives in quantities, and of a purity, useful for industrial bright nickel plating operations.

Both the mono as well as the dimethylol coumarins are crystalline compounds and must be dissolved in the plating bath for use as a brightening agent. Moreover, the addition agent must be added to the bath from time to time as it is consumed. Although the solubility of both mono and dimethylol coumarins is substantial in the usual acid nickel bath, there is always the problem of effecting uniform dissolution of a solid material. This problem is aggravated when the plating operation is under the control of unskilled or only semi-skilled personnel, as is frequently true in large-scale industrial operations. It is preferable, therefore, to have any addition agent in liquid form since this can be more readily measured and added to the plating bath as required, and will more quickly secure uniform concentration of the additive therein. It is accordingly a further object of the present invention to prepare methoylol coumarin in aqueous solution.

In general, the novel method of producing methylol coumarin comprises first reacting coumarin in aqueous solution with an alkali metal hydroxide under controlled conditions of concentration and at elevated temperature; cooling the reaction mixture and further reacting that with formaldehyde while holding the reaction mixture at or near normal ambient room temperature for a predetermined time; cooling the resulting product below ambient and maintaining in the cooled condition while neutralizing with a mineral acid to precipitate methylol coumarin; decanting and filtering to separate the product and then redissolving the product to provide a concentrated aqueous solution.

The process of the invention will be described in more detail with reference to specific processing steps whereby the 6,8-dimethylol coumarin is obtained in good yield.

The first step in the process consists in dissolving and reacting coumarin with an alkali metal hydroxide, such as sodium hydroxide, in aqueous solution to form sodium coumarate. In order to facilitate the dissolution and formation of the sodium salt, the solution is preferably heated to the boiling temperature. In addition, there is a reasonably critical ratio which should be maintained for efiicient reaction, such that there should be present in solution at least two moles of sodium hydroxide for each mole of coumarin, where the desired 6,8-dimethylol coumarin is to be the predominant reaction product.

When the foregoing reaction has gone to completion,

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the mixture is cooled to normal ambient room temperature, i.e. 2530 C., and formaldehyde is added. Two moles of formaldehyde are employed for each mole of coumarin originally dissolved in solution. This mixture is agitated while holding it at the aforesaid ambient room temperature, using external cooling if necessary, and this is maintained for a period of about 46 to 48 hours to get complete reaction.

The reaction products from the step just described are then cooled to a temperature substantially below ambient to stop further reaction and prevent undesirable polymerization. Preferably the temperature here is from -10 to 10 C., and the substituted coumarin is then precipitated by neutralizing with a mineral acid, preferably hydrochloric. The solution is decanted and filtered to separate the precipitated coumarin product which consists predominantly (about 90% or better) of 6,8-dimethylol coumarin, the balance being substantially all 6-methylol coumarin. The precipitate is redissolved in water to any desired concentration for use as the nickel brightening addition agent.

The use of sodium hydroxide for production of the corresponding couma'rate salt is preferred for economic reasons, although other strong alkali metal hydroxides such as potassium or lithium are operative but are less desirable. Apart from higher cost, traces of the cations of these bases may be carried over into the final product and i be objectionable in the plating solution. This same consideration applies also to use of acids other than hydrochloric, although other acids, e.g. sulfuric, phosphoric, acetic, formic, are operative.

What is claimed is:

1. The process of making methylol coumarin which comprises (a) dissolving and reacting coumarin with an alkali metal hydroxide in aqueous solution to form the alkali metal coumarate;

(b) cooling the reaction mixture to ambient room temperature, adding formaldehyde while agitating and maintaining the reaction mixture at such ambient temperature;

(0) cooling the reaction mixture of step (b) substantially below ambient, maintaining it at such reduced temperature while acidifying to neutralize the solution and precipitate methylol coumarin;

(d) decanting the solution and filtering to recover the methylol coumarin.

2. The process as defined in claim 1, wherein the ratio of alkali metal hydroxide to coumarin in step (a) is 2 moles to l.

3. The process as defined in claim 2, wherein the alkali metal hydroxide in step (a) is sodium hydroxide.

4. The process as defined in claim 1, wherein formaldehyde is added in step (b) in the amount of two moles for each mole of coumarin in the starting mixture.

5. The process as defined in claim 1, wherein the reaction mixture of step (b) is agitated and maintained at gmbient room temperature for a period of about 46-48 ours.

6. A process as defined in claim 1, wherein the reduced temperature maintained in step (c) is from about -10 to 10 C.

7. The process as defined in claim 1, wherein the neutralizing acid of step (c) is hydrochloric.

References Cited Lele et al., J. Org. Chem., Vol. 25 (1960), pages 1713-16.

WALTER A. MODANCE, Primary Examiner. JAMES A. PATTEN, Examiner. 

1. THE PROCESS OF MAKING METHYLOL COUMARIN WHICH COMPRISES (A) DISSOLVING AND REACTING COUMARIN WITH AN ALKALI METAL HYDROXIDE IN AQUEOUS SOLUTION TO FORM THE ALKALI METAL COUMARATE, (B) COOLING THE REACTION MIXTURE TO AMBIENT ROOM TEMPERATURE, ADDING FORMALDEHYDE WHILE AGITATING AND MAINTAINING THE REACTION MIXTURE AT SUCH AMBIENT TEMPERATURE; (C) COOLING THE REACTION MIXTURE OF STEP (B) SUBSTANTIALLY BELOW AMBIENT, MAINTAINING IT AT SUCH REDUCED TEMPERATURE WHILE ACIDIFYING TO NEUTRALIZE THE SOLUTION AND PRECIPITATE METHYLOL COUMARIN; (D) DECANTING THE SOLUTION AND FILTERING TO RECOVER THE METHYLOL COUMARIN. 